Field of the Invention
The present invention relates to bio-analytical systems and, more specifically but not exclusively, to flow-based enhancement of specificity for label-free biochemical assays.
Description of the Related Art
This section introduces aspects that may help facilitate a better understanding of the invention(s). Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.
An assay is a procedure in molecular biology that is used to test for and/or measure the activity of a drug or a biochemical in an organism or a biological sample. Various types of biochemical assays, such as immunoassays, DNA-hybridization assays, and receptor-based assays, are widely used to detect trace quantities of specific target substances contained in the sample. For example, an immunoassay uses specific binding of an antibody to its antigen to measure the concentration of a target substance in a biological liquid. Either the antigen or the antibody can serve as the target substance. Other types of assays similarly use other types of specific binding.
A representative biochemical assay employs a solid substrate whose surface is coated with receptors having a relatively high specific binding affinity to a desired target substance. When a liquid sample containing the target substance is applied to the surface, the high specific binding affinity causes the receptors to capture the target substance. A common approach to detecting the captured target substance is to chemically attach to it a label that can be used to generate an observable signal. For example, a label can include a radioactive isotope, an enzyme, a fluorescent molecule, and/or a magnetic particle. The label can be attached to the captured target substance using any suitable means, such as covalent or electrostatic bonding and high-affinity molecular recognition of an exposed part of the target substance. The attached label is then detected using an appropriate detection means corresponding to the type of the label, thereby providing a measure of the concentration of the target substance in the sample.
One problem with biochemical assays in general is the presence of false-positive signals. For example, in the above-described label-based biochemical assays, false positives might originate from non-specific binding of labels to the surface of the solid substrate. Further complications arise when the sample contains several similar or related substances, with the target substance being only one of them. Due to the similarity to the target substance, the related non-target substances might bind, non- or semi-specifically, to the target receptors and then similarly bind the labels, thereby causing a corresponding false-positive signal.